In detergent applications, large volumes of chemicals are used. Because these chemicals may eventually enter the environment and reside in subsurface waters or open bodies of surface waters, it is highly desirable for such chemicals to be degradable in order to eliminate any environmental problems. Traditionally, detergents and cleaning agents have contained phosphates. These phosphates are added as detergent builders, acting to sequester alkaline earth metal hardness ions, as encrustation inhibitors and as antiredeposition agents. Despite the fact that the well known inorganic phosphorus compounds are highly effective and relatively non-toxic, they lead to environmental problems such as causing excess plant growth, resulting in eutrophication of lakes.
During the past three decades, efforts have been made in the detergent industry to convert from the eutrophying polyphosphates to more environmentally acceptable materials such as polycarboxylic acid polymers (e.g., polyacrylic acids). In a similar situation, the ubiquitous branched alkyl benzene sulfonates (ABS), probably the most popular surfactants, were replaced by their biodegradable linear counterparts (LAS) to eliminate build-up in surface and subsurface waters.
While the polycarboxylic acid polymers and copolymers currently used in detergents and water treatment applications do not suffer from the same drawbacks as the phosphorus-containing inorganic builders or the foam producing ABS surfactants, the past has taught it is most desirable that chemicals used in large volume applications which enter the environment be biodegradable. Unfortunately, most polycarboxylic acid polymers and copolymers useful in detergent applications or as dispersants or as water treatment chemicals are not highly biodegradable.
Some effort has been made to provide biodegradable water-soluble polymers through the use of comonomers containing two ethylenically unsaturated double bonds. Notable in this regard is European Patent Application No. 291,808, filed May 7, 1988 (assigned to BASF Aktiengesellschaft). Disclosed in the '808 application are water-soluble copolymers prepared by the copolymerization of monomer mixtures of at least one monoethylenically unsaturated monocarboxylic acid, at least one comonomer containing at least two ethylenically unsaturated non-conjugate double bonds and at least one COO--X group, at least one monoethylenically unsaturated dicarboxylic acid, hydroxyl esters of monoethylenically unsaturated carboxylic acids and other water-soluble monoethylenically unsaturated monomers. However, studies of these polymers have revealed they are difficult to make and do not combine the balance of good performance properties and biodegradability.
U.S. Pat. No. 4,746,456 ('456) discloses a detergent composition containing a graft copolymer of polyalkylene oxides and vinyl acetate which purportedly act as a soil redeposition inhibitor. The detergent composition disclosed in the '456 patent contains from 0.1 to 3% of the graft copolymer obtained from grafting onto a polyalkylene oxide polymer of ethylene oxide, propylene oxide or butylene oxide, vinyl acetate in a weight ratio of from 1:0.2 to 1:10. However, the detergent compositions of the '456 patent still contain phosphate along with this soil redeposition inhibitor and these graft copolymers are not readily biodegradable.
We have now discovered that graft copolymers prepared by grafting acid functional monomers onto biodegradable polyalkylene oxide and polyalkoxylated substrates form graft copolymers which are biodegradable and are useful as detergent additives. These graft copolymers are particularly biodegradable when they are prepared by a process which yields short chain graft units which is obtained by utilizing a metal salt, preferably a salt generating copper ions.